64 BBCWildlife December 2019
H
ow’s this for a hibernation?
In 2012–13, during a
year of failure of their
favourite food, beech
mast, five fat (edible)
dormice from the Vienna
Woods hibernated
continuously for 11 months, with one adult
female inactive for 346 days! That’s not
sleeping away the winter, that’s sleeping
away your life.
This remarkable case illustrates one
thing: hibernation isn’t always what we
think it is. Most of us assume that animals
go to sleep in autumn and wake up again
in spring, when the weather warms up. Butwhile this is broadly true, hibernation is far
more complicated and mysterious than that.
And it is not actually a ‘sleep’ at all.
When a hedgehog dozes off in summer,
for example, its body temperature of
about 35°C will drop a few degrees and
its breathing will be slower but remain
steady and regular. During hibernation,
however, its temperature plummets to
about the level of the outside environment.
Its metabolic rate will be 2 per cent of
its normal summer activity and its heart
rate will drop from 110–150 beats per
minute down to anywhere between 5 and
70 beats per minute. The breathing alters
drastically, too. When awake, a hedgehogbreathes about 25 times a minute
regularly and rhythmically. In
deep hibernation, it can go
two hours without a single
breath and, when it does
resume, it does 40–50 rapid
breaths that tail off until the long
gap to next time. In additiontoall
that, a hedgehog eats feverishlyand
puts on a lot of fat, which it willuseas
a fuel store. These are profound,long-
lasting and deep-seated changes.Whatever
hibernation is, it’s not a sleep.Rise and shine
So, hibernation is a state of deep dormancy
into which an animal locks its body and
throws away the key for a few months,
right? Wrong. Though the physiological
changes are profound, usually no animal in
hibernation remains completely torpid for
more than about 30 days at most, which isIn deep hibernation, a hedgehog can
go two hours without a single breath.